Method for roughening the surface of a metal layer, thin film transistor, and method for fabricating the same

A method for fabricating a thin film transistor, the method comprising:

• forming an oxide semiconductor layer and a source-drain metal layer on an underlying substrate;
• forming a first photo-resist layer on a surface of the source-drain metal layer, and processing the first photo-resist layer by pre-baking, exposing, developing, and post-baking the first photo-resist layer, wherein the post-baking is at a temperature ranging from 110° C. to 150° C.;
• and stripping the first photo-resist layer to roughen the surface of the source-drain metal layer;
• and
• performing a patterning process on the roughened source-drain metal layer, and the oxide semiconductor layer to form patterns of source and drain electrodes, and a pattern of an active layer;
• wherein performing the patterning process on the roughened source-drain metal layer, and the oxide semiconductor layer to form the patterns of the source and drain electrodes, and the pattern of the active layer comprises:
• forming a second photo-resist layer on the roughened source-drain metal layer;
• exposing and developing the second photo-resist layer to form an area where all the second photo-resist is reserved, an area where all the second photo-resist is removed, and an area where a part of the second photo-resist is reserved, wherein the area where a part of the second photo-resist is reserved corresponds to a channel area, and the area where all the second photo-resist is reserved corresponds to the patterns of the source and drain electrodes to be formed;
• in the area where all the second photo-resist is removed, etching the roughened source-drain metal layer and the oxide semiconductor layer to form the pattern of the active layer;
• ashing the second photo-resist layer to remove all of the second photo-resist layer located in the area where a part of the second photo-resist was reserved;
• and subsequently etching in the area where the part of the second photo-resist was reserved to remove the roughened source-drain metal layer to form the patterns of the source and drain electrodes;
• wherein after etching the roughened source-drain metal layer and the oxide semiconductor layer to form the pattern of the active layer, the method further comprises:
• over-etching the roughened source-drain metal layer and the oxide semiconductor layer for a period of time which is 5% to 20% of a length of time of etching the roughened source-drain metal layer and the oxide semiconductor layer.